The prokaryotic heat shock protein DnaJ interacts with the chaperone hsp70-like DnaK protein [ 8016869]. Structurally, the DnaJ protein consists of an N-terminal conserved domain (called 'J' domain) of about 70 amino acids, a glycine-rich region ('G' domain') of about 30 residues, a central domain containing four repeats of a CXXCXGXG motif ('CRR' domain) and a C-terminal region of 120 to 170 residues.
Such a structure is shown in the following schematic representation:
+------------+-+-------+-----+-----------+--------------------------------+
| N-terminal | | Gly-R | | CXXCXGXG | C-terminal |
+------------+-+-------+-----+-----------+--------------------------------+
It is thought that the 'J' domain of DnaJ mediates the interaction with the dnaK protein and consists of four helices, the second of which has a charged surface that includes at least one pair of basic residues that are essential for interaction with the ATPase domain of Hsp70. The J- and CRR-domains are found in many prokaryotic and eukaryotic proteins [1585456], either together or separately. In yeast, J-domains have been classified into 3 groups; the class III proteins are functionally distinct and do not appear to act as molecular chaperones [15170475]. | 
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